Flow Through Pipes MCQ with answer and solution

Concept

Reynolds number is a dimensionless quantity that helps predict flow patterns (laminar or turbulent) in fluid dynamics.

Formula

Re = (V × D) / ν

Step-by-step solution

1. Identify the given parameter values: Pipe diameter D = 300 mm = 0.3 m, Velocity V = 2 m/s, Kinematic viscosity ν = 1 × 10⁻⁶ m²/s. 2. Apply the Reynolds number formula: Re = (V × D) / ν 3. Calculate: Re = (2 m/s × 0.3 m) / (10⁻⁶ m²/s) = 0.6 / 10⁻⁶ = 6 × 10⁵.

Explanation

The Reynolds number (Re) for pipe flow is defined as the ratio of inertial forces to viscous forces, expressed as Re = (V × D) / ν. Substituting the given values (V = 2 m/s, D = 0.3 m, ν = 10⁻⁶ m²/s), we get Re = (2 × 0.3) / 10⁻⁶ = 6 × 10⁵.

Why the other options are wrong

A: Result obtained from incorrect arithmetic operations. B: Value corresponding to neglecting the exponent powers of 10. D: Arrived at if diameter is taken as 0.015 m or wrong power of 10 is used.

Shortcut

Re = (2 × 0.3) × 10⁶ = 0.6 × 10⁶ = 6 × 10⁵.

Common mistake

Forgetting to convert the pipe diameter from mm to meters before calculating.